The invention relates generally to systems and methods for use in treating proliferative tissue disorders, and more particularly to systems and methods for the treatment of such disorders in the breast by positioning tissue and applying radiation.
Malignant tumors are often treated by surgical resection of the tumor to remove as much of the tumor as possible. Infiltration of the tumor cells into normal tissue surrounding the tumor, however, can limit the therapeutic value of surgical resection because the infiltration can be difficult or impossible to treat surgically. Radiation therapy can be used to supplement surgical resection by targeting the residual tumor margin after resection, with the goal of reducing its size or stabilizing it. Radiation therapy can be administered through one of several methods, or a combination of methods, including permanent or temporary interstitial brachytherapy, and external-beam radiation.
Brachytherapy refers to radiation therapy delivered by a spatially confined radioactive material inserted into the body at or near a tumor or other proliferative tissue disease site. For example, brachytherapy is performed by implanting radiation sources directly into the tissue to be treated. Brachytherapy is most appropriate where 1) malignant tumor regrowth occurs locally, within 2 or 3 cm of the original boundary of the primary tumor site; 2) radiation therapy is a proven treatment for controlling the growth of the malignant tumor; and 3) there is a radiation dose-response relationship for the malignant tumor, but the dose that can be given safely with conventional external beam radiotherapy is limited by the tolerance of normal tissue. In brachytherapy, radiation doses are highest in close proximity to the radiotherapeutic source, providing a high tumor dose while sparing surrounding normal tissue. Interstitial brachytherapy is useful for treating malignant brain and breast tumors, among others.
Williams U.S. Pat. No. 5,429,582, entitled “Tumor Treatment,” describes a Brachytherapy method and apparatus for treating tissue surrounding a surgically excised tumor with radioactive emissions to kill any cancer cells that may be present in the tissue surrounding the excised tumor. In order to implement the radioactive emissions, Williams provides a catheter having an inflatable balloon at its distal end that defines a distensible reservoir. Following surgical removal of a tumor, the surgeon introduces the balloon catheter into the surgically created pocket left following removal of the tumor. The balloon is then inflated by injecting a fluid having one or more radionuclides into the distensible reservoir via a lumen in the catheter.
While brachytherapy procedures have successfully treated cancerous tissue, alternative radiation treatments are sometimes preferable, including radiation therapies which are delivered from a source external to the patient. For example, External Beam Radiation Therapy involves directing a “beam” of radiation from outside the patient's body, focused on the target tissue within a patient's body. The procedure is painless and often compared to the experience of having an x-ray.
As with any radiation therapy, the goal is to deliver a prescribed dose of radiation to the target tissue while minimizing damage to healthy tissue. More recent advances in radiation therapy such as Three-Dimensional Conformal Radiation Therapy (3DCRT) and Intensity Modulated Radiation Therapy (IMRT) have increased the precision of external radiation therapy with sophisticated shaping and directing of therapeutic radiation beams. In addition, imaging techniques allow delineation of a more complex planning target volume (“PTV”, PTV refers to the mass of tissue which includes both the residual malignancy as well as a margin of surrounding healthy tissue). These imaging procedures use cross-sectional imaging modalities including computed tomography (CT), magnetic resonance imaging (MRI), positron emission tomography (PET), single photon emission computed tomography (SPECT) and portal imaging to visualize target tissue. Treatment planning software combines the anatomical details from the imaging procedures and a PTV outlined by the physician, to optimize the number, size and shape of the radiotherapy beams used to treat the patient. The goal of the treatment plan is to deliver a conformal radiation dose to the PTV and minimize the radiation delivered to adjacent normal tissue outside the PTV.
In use, 3DCRT provides radiation beams shaped to “conform” to a target tissue volume, and with the ability to visualize and to arrange the radiation therapy beams, physicians can maximize coverage of the target tissue and minimize exposure to normal tissue. IMRT similarly conforms radiation beams to the size, shape and location of the target tissue by using hundreds to thousands of small, modulated radiation beams, striking the target tissue with varying intensities. The multitude of beams treats the target tissue and minimizes damage to healthy tissue. Yet, even the most advanced procedures require the patient and the target tissue to be properly positioned, and in some cases immobilized. Unfortunately, the irregular surface of a cavity created by the resection of tissue can make it difficult for the imaging techniques to determine the exact location of the target tissue, and even with the opportunity to completely map the target area, the unsupported tissue surrounding the resected cavity may shift during the procedure or between imaging and treatment, particularly where the treatment regimen involves radiation doses provided over the course of several days or weeks.
As a result, there is still a need for additional methods for delivering radiation from an external radiation source to tissue adjacent to a resected tissue cavity with a desired accuracy and without over-exposure of surrounding tissue.